Optical furnace



FIG. 1 is a first perspective view of an optical furnace showing our new design.

FIG. 2 is a second perspective view of an optical furnace showing our new design.

FIG. 3 is a third perspective view of an optical furnace showing our new design.

FIG. 4 is a fourth perspective view of an optical furnace showing our new design.

FIG. 5 is a top view of an optical furnace showing our new design; and,

FIG. 6 is a bottom view of an optical furnace showing our new design.

The broken lines shown represent the portions of the optical furnace that form no part of the claimed design. 

CLAIM The ornamental design for an optical furnace, as shown and described. 